Rebellion updates

[Jack Firth]

Hello all! Just wanted to give a quick announcement about some of the new features that have landed in Rebellion recently:

• Added comparators and ranges, allowing you to compare data in arbitrary ways and express ranges of data such as "all integers between 7 and 42, inclusive".
• Added transducers and reducers for sorting sequences as well as finding the max and min, according to an arbitrary comparator.
  
• Record, tuple, and wrapper data types now support pattern matching.
• Added results, which are roughly the same as Haskell's Either data type or Rust's Result data type.
  
• Added atomic fixnums and atomic booleans for safe (and fast!) concurrently-mutable data.
  
• Improved support for contracts, including contracts for options, reducers, comparators, and results.
• Added reducers for more of Racket's standard collections, including vectors, sets, and hash tables.
• Added vector builders for efficiently and safely building a vector of unknown size by inserting elements into it one at a time.

Install it using `raco pkg install --auto rebellion`. Bug reports, feature requests, and patches are all welcome at the github repository.